The treatment of unstable insulin-dependent diabetics (UIDD) is still an unsolved problem. A comparison was made between optimized conventional treatment (OCT) (Ultralente + Actrapid at breakfast, Actrapid at lunch and Actrapid at dinner) and continuous s.c. insulin infusion (CSII) for 30 days in 10 UIDD outpatients. Continuous 24-h blood glucose monitoring with an artificial pancreas, fasting values of HbA1, plasma lipids, growth hormone, glucagon, daily urinary glucose and protein excretion were recorded after each treatment; a daily blood glucose profile was determined every week. Daily mean blood glucose values dropped significantly (p less than 0.01): from 187.2 +/- 66.6 (OCT) to 111.6 +/- 27.0 mg/dl (CSII), and hypoglycemic and ketotic events disappeared during CSII. A significant improvement (p less than 0.01 - p less than 0.001) in all other parameters was also observed. It is suggested that CSII may help to improve metabolic control and the quality of life in UIDD.